The present invention is directed to an improved feed limit switch configuration for a strapping machine. More particularly, the present invention is directed to feed limit switch configurations for a strapping machine that, by action of the switches, eliminated dust and debris from the switches. 
Strapping machines are used for securing straps around loads. Known strappers include a strapping head and drive mechanism mounted within a frame. Strapping material is fed from a supply (e.g., a dispenser) into a chute that is mounted to the frame. A typical drive mechanism includes feed wheels that “push” the material through the chute via the strapping head. The leading end of the strapping material traverses the chute and re-enters the strapping head at the end of the chute. 
A number of functions are carried out within the strapping head. First, the strapping material that “reenters” the chute is gripped by a gripper when the strap reaches and contacts a limit switch. With the leading end gripped, the strap is rewound and tensioned around the load. The strapping head also includes a cutter to cut the strap from the strap source or supply and a sealer to seal an overlying course of strapping material onto itself. This seal is commonly referred to as a weld and is effected by heating overlying courses of the strap by use of a vibrating element. 
In order to provide a seal of the highest integrity, it is important to assure that a sufficient amount of (leading end) strap is provided onto which the trailing end strap is welded. As such, it is necessary to assure that the leading end of the strap has traveled sufficiently “far” into the strapping head. At the point at which the strap reaches its predetermined depth of travel into the head, a limit switch is contacted. Typically, such limit switches are sliding elements that generates a signal when in one sliding position, and terminates the signal when in the other of the sliding positions. 
It will, however, be recognized that the environment in which strapping machines operate may be less than optimal vis-a-vis equipment operation, instrumentation, control and switching. This is due in large part to the dust and debris that is associated with the goods being strapped, as well as the strapping material itself.  
Efforts have been made to prevent dust and debris from affecting the proper operation of these sliding switches. For example, seals can be positioned about the juncture of the sliding portions of the switch and the housing in which it slides. Lubricants and the like have also been used (in conjunction with seals) to prevent the introduction of contaminants. While these efforts have met with some success in limiting the ingress of contamination, they nevertheless require monitoring and maintenance to assure proper operation. 
Other arrangements use compressed air to clear the spaces in and around the sliding portions of the switch to prevent the accumulation of dust and debris. Again, although these arrangements have been successful in preventing the accumulation of contaminants, these arrangements require monitoring and maintenance to assure proper operation. 
Accordingly, there exists a need for a limit switch assembly that limits the introduction of contaminants to the components of strapping machine limit switches. Desirably, such a limit switch assembly prevents the accumulation of dust and debris in the pockets formed by the sliding switch components. Most desirably, such a limit switch configuration is self cleaning in that it clears dust and debris during normal switch (sliding) operation. 